Time-of-flight mass spectrometer

ABSTRACT

A no-electric field region (246A) and an electric field region (246B) are formed in a flight tube (246). In the no-electric field region (246A), ions introduced from an ion emission unit fly. In the electric field region (246B), a reflectron (244) is provided and the ions having passed through the no-electric field region (246A) are reflected to the no-electric field region (246A) by an action of an electric field formed on an inner side of a plurality of electrodes (244A, 244B). A through-hole (246D) is formed in at least a part of the flight tube (246) to be closer to the electric field region (246B) than the no-electric field region (246A).

TECHNICAL FIELD

The present invention relates to a time-of-flight mass spectrometerincluding a hollow flight tube into which ions emitted from an ionemission unit are introduced.

BACKGROUND ART

In a time-of-flight mass spectrometer (TOFMS), ions to be analyzed areemitted from an ion emission unit, and the ions fly in a hollow flighttube and then are detected by a detector. As a result, the time offlight of the ion until the ion reaches the detector is measured, andthe mass-to-charge ratio m/z of the ion is calculated on the basis ofthe time of flight (for example, refer to Patent Documents 1 and 2).

The flight tube is provided in a vacuum chamber. A vacuum vessel thatbecomes in a vacuum state during analysis is formed in the vacuumchamber, the flight tube is provided in the vacuum vessel, and therebythe flight tube also becomes in a vacuum state during analysis.

A reflectron is provided in the flight tube. The reflectron isconfigured by coaxially arranging a plurality of loop electrodes. Byapplying a voltage to each of these electrodes, an electric field isformed on an inner side of each electrode (inner side of thereflectron).

The ions introduced from the ion emission unit into the flight tube passthrough a no-electric field region where no reflectron is provided, andthen fly to an electric field region formed on the inner side of thereflectron. In the electric field region, the ions are reflected by theaction of the electric field and are again guided to the no-electricfield region, and the ions having passed through the no-electric fieldregion are detected by the detector.

In the time-of-flight mass spectrometers disclosed in Patent Documents 1and 2, a so-called dual stage reflectron is used. In this type ofreflectron, among a plurality of electrodes constituting thecorresponding reflectron, a first stage is composed of a part of theelectrodes on the no-electric field region side, and a second stage iscomposed of the remaining electrode (a part of the electrodes on a sideopposite to the no-electric field region side). The voltages to beapplied to the electrodes constituting the first stage and the secondstage are different. Therefore, electric fields having differentpotential distributions are formed in the first stage and the secondstage.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent No. 5924387

Patent Document 2: Japanese Patent No. 5862791

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In order to realize high resolution, it is extremely important that thepositional relationship between the electrodes constituting the secondstage and the ion emission unit is accurate. Therefore, the flight tubeis formed to extend to the end of the reflectron, and the reflectron isconfigured to be in the flight tube by stacking the electrodes towardthe ion emission unit with reference to the end position.

However, in a case where the flight tube is formed to extend to the endof the reflectron as described above, when the vacuum vessel is broughtinto a vacuum state, the outflow of gas in the flight tube becomesworse. As a result, there is a problem that the degree of vacuum in theelectric field region formed on the inner side of the reflectron islowered and the resolution is lowered. In particular, since at the endportion of the reflectron, the kinetic energy of the ions is small andan adverse effect due to collision with gas is likely to occur, when thedegree of vacuum is lowered at this portion, the deterioration of theperformance such as resolution becomes remarkable.

Further, each electrode constituting the reflectron is supplied withpower from a voltage divider through a wiring. In order to check theconnection status of the wiring connected to each electrode, checkwhether there is misalignment in each electrode, and check for otherabnormalities, it is preferable that the reflectron can be visuallyobserved directly from the outside. However, in the configuration inwhich the reflectron is covered with the flight tube, the reflectroncannot be easily visually observed from the outside.

The invention has been made in view of the above circumstances, and anobject thereof is to provide a time-of-flight mass spectrometer whichcan improve the degree of vacuum in an electric field region formed onan inner side of a reflectron. Another object of the invention is toprovide a time-of-flight mass spectrometer in which the reflectron canbe easily visually observed from the outside.

Means for Solving the Problems

(1) A time-of-flight mass spectrometer according to the inventionincludes an ion emission unit, a flight tube, a reflectron, and a vacuumchamber. The ion emission unit emits ions to be analyzed. The flighttube is hollow, and the ions emitted from the ion emission unit areintroduced into the flight tube. The reflectron is provided in theflight tube, and is configured by coaxially arranging a plurality ofloop electrodes. A vacuum vessel that becomes in a vacuum state duringanalysis is formed in the vacuum chamber, and the flight tube isprovided in the vacuum vessel.

A no-electric field region and an electric field region are formed inthe flight tube. In the no-electric field region, the ions introducedfrom the ion emission unit fly. In the electric field region, thereflectron is provided and the ions having passed through theno-electric field region are reflected to the no-electric field regionby an action of an electric field formed on an inner side of theplurality of electrodes. A first through-hole is formed in at least apart of the flight tube to be closer to the electric field region thanthe no-electric field region.

With such a configuration, since the first through-hole is formed in atleast a part of the flight tube to be closer to the electric fieldregion than the no-electric field region, when the vacuum vessel isbrought into a vacuum state, the gas in the flight tube can be easilyreleased via the first through-hole. Thereby, the degree of vacuum ofthe electric field region formed on the inner side of the reflectron canbe improved. As a result, retention of the ions in the flight tube iseliminated, and the reduction in resolution and sensitivity can beprevented.

Further, the reflectron provided in the flight tube can be easilyvisually observed from the outside via the first through-hole formed onthe flight tube. As a result, since it becomes easy to check theconnection status of the wiring connected to each of the electrodesconstituting the reflectron, check whether there is misalignment in eachof the electrodes, and check for other abnormalities, themaintainability is improved.

(2) The flight tube may have a tubular side wall. In this case, thefirst through-hole may be formed on the side wall.

With such a configuration, the gas in the flight tube can be easilyreleased via the first through-hole formed on the side wall of theflight tube, and the reflectron provided in the flight tube can beeasily visually observed from the side.

(3) The electric field region may include a first region where the ionshaving passed through the no-electric field region are decelerated, anda second region where the ions decelerated in the first region arereflected. In this case, the first through-hole may be formed on theside wall at a position facing at least the second region.

With such a configuration, among the first region (first stage) and thesecond region (second stage) constituting the electric field region, thegas in the flight tube can be easily released in the second region, andthe reflectron can be easily visually observed from the side in thesecond region. Since the release of the gas in the flight tube becomesparticularly bad on the second region side, the degree of vacuum of theelectric field region can be effectively improved by forming the firstthrough-hole at a position facing the second region.

(4) The flight tube may be formed in a bottomed tubular shape having abottom surface on the electric field region side. In this case, thefirst through-hole may be formed on the bottom surface.

With such a configuration, the gas in the flight tube can be easilyreleased via the first through-hole formed on the bottom surface of theflight tube, and the reflectron provided in the flight tube can beeasily visually observed from the bottom surface side.

(5) A second through-hole may be formed on the vacuum chamber at aposition facing at least a part of the first through-hole.

With such a configuration, the reflectron provided in the flight tubecan be easily visually observed from the outside of the vacuum chambervia the first through-hole and the second through-hole at leastpartially facing each other. A third through-hole different from thesecond through-hole may be formed on the vacuum chamber. In this case,the time-of-flight mass spectrometer may further include a lid memberthat closes the second through-hole, and a vacuum pump connected to thethird through-hole.

(6) The time-of-flight mass spectrometer may further include a voltagedivider. The voltage divider is provided in the flight tube, and appliesvoltages divided using a plurality of resistors to the plurality ofelectrodes. In this case, the first through-hole may be formed at aposition facing at least a part of the plurality of resistors.

With such a configuration, since the first through-hole is formed on theflight tube at a position facing at least a part of the plurality ofresistors, the influence of radiant heat from the resistors to theflight tube can be suppressed, and thermal expansion of the flight tubecan be prevented. Accordingly, since it is possible to prevent the timeof flight of the ions in the flight tube from fluctuating due to thethermal expansion of the flight tube, the measurement accuracy isimproved.

Effects of the Invention

According to the invention, since the gas in the flight tube can beeasily released via the first through-hole when the vacuum vessel isbrought into a vacuum state, the degree of vacuum of the electric fieldregion formed on the inner side of the reflectron can be improved.Further, according to the invention, the reflectron provided in theflight tube can be easily visually observed from the outside via thefirst through-hole formed on the flight tube.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a configuration example of aliquid chromatograph mass spectrometer including a time-of-flight massspectrometer according to an embodiment of the invention.

FIG. 2 is a schematic diagram illustrating a specific configurationaround a flight tube.

FIG. 3 is a schematic diagram illustrating a first modification exampleof a configuration around the flight tube.

FIG. 4 is a schematic diagram illustrating a second modification exampleof a configuration around the flight tube.

MODE FOR CARRYING OUT THE INVENTION 1. Overall Configuration of LiquidChromatograph Mass Spectrometer

FIG. 1 is a schematic diagram illustrating a configuration example of aliquid chromatograph mass spectrometer including a time-of-flight massspectrometer according to an embodiment of the invention. The liquidchromatograph mass spectrometer includes a liquid chromatograph unit 1and a mass spectrometer unit 2.

The liquid chromatograph unit 1 includes a mobile phase container 10, apump 11, an injector 12, a column 13, and the like. A mobile phase isstored in the mobile phase container 10. The pump 11 sends out themobile phase in the mobile phase container 10 to the injector 12. In theinjector 12, a predetermined amount of sample is injected into themobile phase from the mobile phase container 10. The mobile phase intowhich the sample is injected is introduced into the column 13, andrespective components in the sample are separated in the course ofpassing through the column 13. The respective components in the sampleseparated by the column 13 are sequentially supplied to the massspectrometer unit 2.

The mass spectrometer unit 2 is configured by a time-of-flight massspectrometer (TOFMS), and an ionization chamber 20, a first intermediatechamber 21, a second intermediate chamber 22, a third intermediatechamber 23, an analysis chamber 24, and the like are formed inside themass spectrometer unit 2. The inside of the ionization chamber 20 issubstantially at atmospheric pressure. Each of the first intermediatechamber 21, the second intermediate chamber 22, the third intermediatechamber 23, and the analysis chamber 24 is brought into a vacuum state(negative pressure state) by driving a vacuum pump (not illustrated).The ionization chamber 20, the first intermediate chamber 21, the secondintermediate chamber 22, the third intermediate chamber 23, and theanalysis chamber 24 communicate with each other, and are configured suchthat the degree of vacuum is gradually increased in this order.

The ionization chamber 20 is provided with a spray 201 such as anelectro spray ionization (ESI) spray. A sample liquid containingrespective components in the sample supplied from the liquidchromatograph unit 1 is sprayed into the ionization chamber 20 by thespray 201 while being charged. As a result, ions derived from therespective components in the sample are generated. However, theionization method used in the mass spectrometer unit 2 is not limited tothe ESI, and other ionization methods such as atmospheric pressurechemical ionization (APCI) or probe electro spray ionization (PESI) maybe used.

The first intermediate chamber 21 communicates with the ionizationchamber 20 via a heating capillary 202 composed of a small-diametertube. Further, the second intermediate chamber 22 communicates with thefirst intermediate chamber 21 via a skimmer 212 composed of a smallhole. The first intermediate chamber 21 and the second intermediatechamber 22 are respectively provided with ion guides 211 and 221 each ofwhich is for focusing the ions and sending the ions to the subsequentstage.

The third intermediate chamber 23 is provided with, for example, aquadrupole mass filter 231 and a collision cell 232. A collision induceddissociation (CID) gas such as argon or nitrogen is continuously orintermittently supplied to the inside of the collision cell 232. Amultipole ion guide 233 is provided in the collision cell 232.

The ions flowing from the second intermediate chamber 22 to the thirdintermediate chamber 23 are separated by the quadrupole mass filter 231according to the mass-to-charge ratio, and only the ions having aspecific mass-to-charge ratio pass through the quadrupole mass filter231. The ions that have passed through the quadrupole mass filter 231are introduced into the collision cell 232 as precursor ions, and arebrought into contact with the CID gas to be cleaved to generate productions. The generated product ions are temporarily held by the multipoleion guide 233, and emitted from the collision cell 232 at apredetermined timing.

A transfer electrode unit 240 is provided in the third intermediatechamber 23 and the analysis chamber 24 so as to straddle the chambers.The transfer electrode unit 240 includes one or a plurality of firstelectrodes 234 provided in the third intermediate chamber 23 and one ora plurality of second electrodes 241 provided in the analysis chamber24. The first electrode 234 and the second electrode 241 are each formedin a loop shape and are coaxially arranged. The ions (product ions)emitted from the collision cell 232 are focused by passing through theinner side of the plurality of electrodes 234 and 241 in the transferelectrode unit 240.

In addition to the second electrode 241, an orthogonal acceleration unit242, an acceleration electrode unit 243, a reflectron 244, a detector245, a flight tube 246, and the like are provided in the analysischamber 24. The flight tube 246 is, for example, a hollow member ofwhich both ends are open, and the reflectron 244 is arranged inside theflight tube 246.

The ions enter the orthogonal acceleration unit 242 from the transferelectrode unit 240. The orthogonal acceleration unit 242 includes a pairof electrodes 242A and 242B facing each other with a space therebetween.The pair of electrodes 242A and 242B extends parallel to an incidentdirection of the ions from the transfer electrode unit 240, and anorthogonal acceleration region 242C is formed between the electrodes242A and 242B.

One electrode 242B is configured by a grid electrode having a pluralityof openings. The ions that enter the orthogonal acceleration region 242Care accelerated in a direction orthogonal to the incident direction ofthe ions, pass through the openings of the one electrode 242B, and areguided to the acceleration electrode unit 243. In the presentembodiment, the orthogonal acceleration unit 242 constitutes an ionemission unit that emits ions to be analyzed. The ions emitted from theorthogonal acceleration unit 242 are further accelerated by theacceleration electrode unit 243, and are introduced into the flight tube246.

The reflectron 244 provided in the flight tube 246 includes one or aplurality of first electrodes 244A and one or a plurality of secondelectrodes 244B. The first electrode 244A and the second electrode 244Bare each formed in a loop shape and are coaxially arranged along theaxis of the flight tube 246. Different voltages are applied to the firstelectrode 244A and the second electrode 244B, respectively.

The ions introduced into the flight tube 246 are guided into a flightspace formed in the flight tube 246, fly into the flight space, and thenenter the detector 245. Specifically, the ions introduced into theflight tube 246 are turned in a U shape to enter the detector 245 bybeing decelerated in a first region (first stage) 244C formed on theinner side of the first electrode 244A, and then being reflected in asecond region (second stage) 244D formed on the inner side of the secondelectrode 244B.

The time of flight from when the ion is emitted from the orthogonalacceleration unit 242 to when the ion enters the detector 245 depends onthe mass-to-charge ratio of the ion. Therefore, the mass-to-charge ratioof each ion can be calculated based on the time of flight of each ionemitted from the orthogonal acceleration unit 242, and the mass spectrumcan be created.

2. Specific Configuration around Flight Tube

FIG. 2 is a schematic diagram illustrating a specific configurationaround the flight tube 246. The flight tube 246 is provided in a vacuumchamber 247. A vacuum vessel 247A that becomes in a vacuum state duringanalysis is formed in the vacuum chamber 247, and the flight tube 246 isprovided in the vacuum vessel 247A. In the present embodiment, thevacuum vessel 247A is the above-mentioned analysis chamber 24.

In the flight tube 246, the reflectron 244 is provided at a positionbiased to a side opposite to the orthogonal acceleration unit 242 side(the ion emission unit side). Thereby, in the flight tube 246, a region(no-electric field region 246A) where the reflectron 244 is not providedand a region (electric field region 246B) where the reflectron 244 isprovided are formed sequentially from the orthogonal acceleration unit242 side.

The no-electric field region 246A is a region where the electric fielddue to the reflectron 244 does not act or is hard to act. The ionsintroduced from the orthogonal acceleration unit 242 into the flighttube 246 fly straight in the no-electric field region 246A and enter theelectric field region 246B in the reflectron 244. In the electric fieldregion 246B, an electric field is formed on the inner side of theplurality of electrodes 244A and 244B. The ions that have passed throughthe no-electric field region 246A are reflected to the no-electric fieldregion 246A by the action of the electric field formed in the electricfield region 246B.

The electric field region 246B includes the above-described first region(first stage) 244C and second region (second stage) 244D. The electricfield formed in the first region 244C is stronger than the electricfield formed in the second region 244D.

An end surface opening of the flight tube 246 on the electric fieldregion 246B side is covered with an end electrode 244E. The endelectrode 244E is attached to the end surface of the flight tube 246 viaan insulation member 244F. The electrodes 244A and 244B of thereflectron 244 are sequentially stacked from the end electrode 244E viaan insulation member 244G. In this way, the reflectron 244 is arrangedin the flight tube 246 with high positional accuracy by being stackedwith the end electrode 244E as a reference.

In the present embodiment, a through-hole (first through-hole) 246D isformed on a tubular side wall 246C of the flight tube 246. Thethrough-hole 246D is formed in at least a part of the side wall 246C ofthe flight tube 246 to be closer to the electric field region 246B thanthe no-electric field region 246A. That is, on the side wall 246C of theflight tube 246, the through-hole 246D is formed only at a positionfacing the electric field region 246B, and the through-hole 246D is notformed at a position facing the no-electric field region 246A.

More specifically, the through-hole 246D is formed on the side wall 246Cof the flight tube 246 at a position facing the second region 244D.Thus, the through-hole 246D is preferably formed in the vicinity of theend of the flight tube 246 on a side opposite to the orthogonalacceleration unit 242 side (ion emission unit side). However, thethrough-hole 246D may be formed to straddle from the position facing thesecond region 244D on the side wall 246C of the flight tube 246 to aposition facing the first region 244C. Further, the number ofthrough-holes 246D is not limited to one, and a plurality ofthrough-holes 246D may be formed.

In the vacuum chamber 247, a through-hole (second through-hole) 247B isformed at a position facing at least a part of the through-hole 246Dformed on the flight tube 246. That is, the through-holes 246D and 247Bare provided close to each other such that a part or all of thethrough-hole 246D formed on the flight tube 246 can be seen when thethrough-hole 247B is viewed from the outside of the vacuum chamber 247along a penetration direction of the through-hole 247B. The through-hole247B can be closed by a lid member (not illustrated) that can beattached to and detached from the vacuum chamber 247.

In the present embodiment, a voltage is applied to each of theelectrodes 244A and 244B of the reflectron 244 by a voltage divider244H. A plurality of resistors R are mounted on the voltage divider244H, and the voltages divided by the resistors R are applied to theelectrodes 244A and 244B.

The voltage divider 244H is provided ins the flight tube 246 and isconfigured integrally with the electrodes 244A and 244B. Morespecifically, the voltage divider 244H extends parallel to the side wall246C of the flight tube 246, and is arranged to be close to the sidewall 246C such that a mounting surface on which the resistors R aremounted faces the side wall 246C.

The through-hole 246D formed on the flight tube 246 faces at least apart of the plurality of resistors R. That is, the voltage divider 244His arranged such that a part or all of the plurality of resistors R canbe seen when the through-hole 246D is viewed from the outside of theflight tube 246 along the penetration direction of the through-hole246D.

3. Effects

(1) In the present embodiment, since the through-hole 246D is formed inat least a part of the flight tube 246 to be closer to the electricfield region 246B than the no-electric field region 246A, when thevacuum vessel 247A is brought into a vacuum state, the gas in the flighttube 246 can be easily released via the through-hole 246D. Thereby, thedegree of vacuum of the electric field region 246B formed on the innerside of the reflectron 244 can be improved. As a result, retention ofthe ions in the flight tube 246 is eliminated, and the reduction inresolution and sensitivity can be prevented.

(2) Further, the reflectron 244 provided in the flight tube 246 can beeasily visually observed from the outside via the through-hole 246Dformed on the flight tube 246.

As a result, since it becomes easy to check the connection status of thewiring connected to each of the electrodes 244A and 244B constitutingthe reflectron 244, check whether there is misalignment in each of theelectrodes 244A and 244B, and check for other abnormalities, themaintainability is improved.

(3) In the present embodiment, the through-hole 246D is formed on theside wall 246C of the flight tube 246. Therefore, the gas in the flighttube 246 can be easily released via the through-hole 246D, and thereflectron 244 provided in the flight tube 246 can be easily visuallyobserved from the side.

(4) Further, in the present embodiment, the through-hole 246D is formedon the side wall 246C of the flight tube 246 at a position facing thesecond region 244D. Therefore, among the first region 244C and thesecond region 244D constituting the electric field region 246B, the gasin the flight tube 246 can be easily released in the second region 244D,and the reflectron 244 can be easily visually observed from the side inthe second region 244D.

Since the release of the gas in the flight tube 246 becomes particularlybad on the second region 244D side, the degree of vacuum of the electricfield region 246B can be effectively improved by forming thethrough-hole 246D at a position facing the second region 244D.

(5) Further, in the present embodiment, the through-hole 247B of thevacuum chamber 247 is formed at a position facing the through-hole 246Dof the flight tube 246. Thereby, the reflectron 244 provided in theflight tube 246 can be easily visually observed from the outside of thevacuum chamber 247 via the through-hole 246D and the through-hole 247Bfacing each other.

(6) Further, in the present embodiment, since the through-hole 246D isformed on the flight tube 246 at a position facing at least a part ofthe plurality of resistors R, the influence of radiant heat from theresistors R to the flight tube 246 can be suppressed, and thermalexpansion of the flight tube 246 can be prevented. Accordingly, since itis possible to prevent the time of flight of the ions in the flight tube246 from fluctuating due to the thermal expansion of the flight tube246, the measurement accuracy is improved.

4. Modification Example

FIG. 3 is a schematic diagram illustrating a first modification exampleof a configuration around the flight tube 246. In this modificationexample, the shape of the flight tube 246 and the positions of thethrough-holes 246D and 247B are different from those in the aboveembodiment. In the drawing, the same reference numerals are given to theconfigurations similar to those in the above-described embodiment, anddetailed description thereof will be omitted.

The flight tube 246 in FIG. 3 is formed in a bottomed tubular shapehaving a bottom surface 246E at the end portion on the electric fieldregion 246B side. That is, the end portion of the flight tube 246 on theelectric field region 246B side is closed by the bottom surface 246E,and the end electrode 244E illustrated in FIG. 2 is omitted. Theelectrodes 244A and 244B of the reflectron 244 are sequentially stackedfrom the bottom surface 246E via the insulation member 244G.

A through-hole (first through-hole) 246F is formed in the center of thebottom surface 246E of the flight tube 246. This through-hole 246F islocated closer to the electric field region 246B than the no-electricfield region 246A in the flight tube 246.

In the vacuum chamber 247, a through-hole (second through-hole) 247C isformed at a position facing at least a part of the through-hole 246Fformed on the flight tube 246. That is, the through-holes 246F and 247Care provided close to each other such that a part or all of thethrough-hole 246F formed on the flight tube 246 can be seen when thethrough-hole 247C is viewed from the outside of the vacuum chamber 247along the penetration direction of the through-hole 247C.

In this modification example, the gas in the flight tube 246 can beeasily released via the through-hole 246F formed on the bottom surface246E of the flight tube 246, and the reflectron 244 provided in theflight tube 246 can be easily visually observed from the bottom surface246E side.

FIG. 4 is a schematic diagram illustrating a second modification exampleof a configuration around the flight tube 246. This modification exampleis different from the above embodiment in that a through-hole 247D(third through-hole) different from the through-hole 247B (secondthrough-hole) is formed in the vacuum chamber 247. In the drawing, thesame reference numerals are given to the configurations similar to thosein the above-described embodiment, and detailed description thereof willbe omitted.

The through-hole 247B is closed by an attachable and detachable lidmember 248. A vacuum pump 249 is connected to the through-hole 247D. Thevacuum pump 249 is configured by, for example, a turbo molecular pump.By discharging the gas in the vacuum chamber 247 and the flight tube 246using the vacuum pump 249, the inside of the vacuum chamber 247 and theflight tube 246 is made to reach a predetermined degree of vacuum.However, the position where the through-hole 247D is formed in thevacuum chamber 247 is not limited to the position illustrated in FIG. 4.

As described above, according to the mode in which the through-hole 247Ddifferent from the through-hole 247B is formed in the vacuum chamber 247and the vacuum pump 249 is connected to the vacuum chamber 247 by usingthe through-hole 247D, the inside of the vacuum chamber 247 can beeasily visually observed only by removing the lid member 248 that closesthe through-hole 247B without removing the vacuum pump 249 from thevacuum chamber 247, and the maintainability can be further improved. Inthe configuration as illustrated in FIG. 3, a through-hole differentfrom the through-hole 247C (second through-hole) may be formed in thevacuum chamber 247, and the vacuum pump 249 may be connected to thevacuum chamber 247 by using the through-hole.

However, the invention is not limited to such a configuration, and thevacuum pump 249 can be connected to the vacuum chamber 247 by using thethrough-hole 247B or the through-hole 247C in the above embodiment.

In the above embodiment, the case where the ion emission unit that emitsthe ions to be analyzed is configured by the orthogonal accelerationunit 242 has been described. However, the invention is not limited tothe orthogonal acceleration time-of-flight mass spectrometer, and can beapplied to a linear acceleration time-of-flight analyzer.

Further, the time-of-flight mass spectrometer according to the inventionis not limited to the one configured as a liquid chromatograph massspectrometer by being connected to the liquid chromatograph unit 1, andmay be configured so as not to be connected to the liquid chromatographunit 1 such as a configuration using, for example, matrix assisted laserdesorption/ionization (MALDI).

DESCRIPTION OF REFERENCE SIGNS

-   1 liquid chromatograph unit-   2 mass spectrometer unit-   242 orthogonal acceleration unit-   244 reflectron-   244A first electrode-   244B second electrode-   244C first region-   244D second region-   244E end electrode-   244F insulation member-   244G insulation member-   244H voltage divider-   246 flight tube-   246A no-electric field region-   246B electric field region-   246C side wall-   246D through-hole-   246E bottom surface-   246F through-hole-   247 vacuum chamber-   247A vacuum vessel-   247B through-hole-   247C through-hole-   247D through-hole-   248 lid member-   249 vacuum pump

1. A time-of-flight mass spectrometer comprising: an ion emission unitthat emits ions to be analyzed; a hollow flight tube into which the ionsemitted from the ion emission unit are introduced; a reflectron which isprovided in the flight tube, and is configured by coaxially arranging aplurality of loop electrodes; and a vacuum chamber in which a vacuumvessel that becomes in a vacuum state during analysis is formed and theflight tube is provided in the vacuum vessel, wherein a no-electricfield region where the ions introduced from the ion emission unit fly,and an electric field region where the reflectron is provided and theions having passed through the no-electric field region are reflected tothe no-electric field region by an action of an electric field formed onan inner side of the plurality of electrodes are formed in the flighttube, and a first through-hole is formed in at least a part of theflight tube to be closer to the electric field region than theno-electric field region.
 2. The time-of-flight mass spectrometeraccording to claim 1, wherein the flight tube has a tubular side wall,and the first through-hole is formed on the side wall.
 3. Thetime-of-flight mass spectrometer according to claim 2, wherein theelectric field region includes a first region where the ions havingpassed through the no-electric field region are decelerated, and asecond region where the ions decelerated in the first region arereflected, and the first through-hole is formed on the side wall at aposition facing at least the second region.
 4. The time-of-flight massspectrometer according to claim 1, wherein the flight tube is formed ina bottomed tubular shape having a bottom surface on the electric fieldregion side, and the first through-hole is formed on the bottom surface.5. The time-of-flight mass spectrometer according to claim 1, wherein asecond through-hole is formed on the vacuum chamber at a position facingat least a part of the first through-hole.
 6. The time-of-flight massspectrometer according to claim 1, further comprising: a voltage dividerwhich is provided in the flight tube and applies voltages divided usinga plurality of resistors to the plurality of electrodes, wherein thefirst through-hole is formed at a position facing at least a part of theplurality of resistors.
 7. The time-of-flight mass spectrometeraccording to claim 5, wherein a third through-hole different from thesecond through-hole is formed on the vacuum chamber.
 8. Thetime-of-flight mass spectrometer according to claim 7, furthercomprising: a lid member that closes the second through-hole; and avacuum pump connected to the third through-hole.